1. Field of the Invention
The present invention is directed to apparatus for measuring leakage of fluids from a closed container and more particularly to a temperature compensated pressure indicator adapted to be mounted within a pressurized container.
2. Description of the Prior Art
A large number of applications utilizing a closed vessel or a pressurized container require an indication of the pressure level within the container. Frequently, these vessels or containers are employed to maintain a relatively high pressure; e.g., 7000 psi over a long period of time and are subject to sudden temperature changes. For example, in the field of fire extinguishers, it is quite common to utilize a conventional fire extinguisher having a pressure of about 600 psi or greater that can be subject to losses of pressure due to leakages of the fluid in the container. Other applications exist in a large number of fields such as monitoring floatation and impact bags in aircraft and other vehicles. Such leakages may occur due, for example, to accidental droppage of the container by a maintenance man or for numerous other reasons. Such a container may be rendered useless if its fire extinguishing fluid leaks appreciably. If the fire extinguisher containers are utilized, for example, in aircraft or other vehicles, it is quite apparent that a hazardous condition can develop on account of such leakage.
Other sources of leakage from a container may be due to microscopic openings in the metal from which the container is made, flaws in the welding material which are not readily detectable, fatigue of the material of the container because of the stresses and strains, and numerous other factors. Any or all these factors may be coexistent and may materially effect adversely the operativeness and utility of the container for its primary and essential functions.
One particular leakage indicator for fire extinguishers is shown in U.S. Pat. No. 3,735,376 issued on May 22, 1973, and assigned to the assignee of the present application. The device of the U.S. Pat. No. 3,735,376 provided a temperature compensation alarm mechanism for a fire extinguisher suitable for use on aircraft or other vehicles.
The mechanism included in addition to the main container, a miniaturized container which was inserted into the main container and was effectively separated by a diaphragm between the two containers. The diaphragm was responsive to a predetermined droppage in pressure of the main container to produce a signal indicative that the fire extinguisher was leaking. Since both the miniature container and the main container were filled with fluids having similar pressure temperature responses, the device was essentially temperature independent.
This device solved the problem of providing apparatus that could automatically determine a leakage or inoperative condition in a fire extinguisher or other pressure containers. The arrangement could serve to inform the staff of an aircraft that a defective condition had developed and in commercial use, the staff of the aircraft could signal the nearest landing field that the fire extinguisher may need prompt replacement or repair.
Other forms of pressure sensor devices have existed in the patents of the prior art such as the U.S. Pat. No. 3,576,412 issued Apr. 27, 1971. Problems existed in these devices of the prior art; for example, it was difficult to calibrate the pressure sensitivity and further to determine the operativeness of the switching mechanism of the leakage detector when it was installed or after a prolonged period in service. In addition, most prior art switches added an additional failure component to the pressure system and provide a thermal lag factor when subject to sudden temperature changes.